Radial scanning television system



June 27, 1939. L 5 FOREST 2,163,749

RADIAL SCANNING TELEVISION SYSTEM Filed March 21, 1936 3 Sheets-Sheet 1 INVENTOR.

Lee de Fbrest ATTORNEYS June 27, 1939.

v L. DE FOREST RADIAL SCANNING TELEVISION SYSTEM Filed March 21, 1956 s Sheets-Sheet 2 POTENTIAL on GRID OPSI K 0? m5 E6 wr e d e 6 L ATTORNEYS June 27, 1939. DE FOREST RADIAL SCANNING TELEVISION SYSTEM [TRANSNTTER 3 Sheets-Sheet 3 Filed March 21, 1936 F J- S 73 M nimum l-l'l 57 APPUFIER AIIPUFIER RADIO 6 rll W L I? w RAD") TRANSMKTTE Fl LTE FILTER Lee de Fbresz Patented June 27, 1939 UNITED STATES PATENT OFFICE RADIAL SCANNING TELEVISION SYSTEM Application March 21, 1936, Serial No. 70,061

11 Claims.

This invention relates to a television system in which a single vibrating mirror may be used to scan both dimensions of the transmitted or reproduced image. In another aspect it relates f.- to the use of such a single vibrating mirror system in such manner as to provide stereoscopic television images, that is images which have the visual effect of a third dimension or depth. An essential feature of both aspects of my invention I is the use of a vibrating mirror which is rotated at the same time that it is vibrating, causing it to scan the image on the reproducing screen in radial lines. I have therefore called my new invention a radial scanning television system, in

tending to embrace by this term both the fundamental idea of radial scanning and the application of this idea to a system which will reproduce television signals with a stereoscopic efiect.

An object of my invention is to provide a television system which will be economical and efficient in construction and operation and which will give increased detail and greater illumination at the center of the viewing screen, and which may produce stereoscopic images.

' A feature of my invention is the provision of a mirror mounted on a torsional vibrating member having a fixed resonant frequency, providing means to excite the vibrating system at its resonant frequency, and mounting the entire mirror,

" vibrating system, and exciting means for rotation at a constant frequency bearing a fixed relationship to the picture frequency of the system and to the resonant frequency of the vibrating member.

Another feature of my invention is the provision of means cooperating with the rotating means just discussed to produce an exciting frequency equal to the resonant frequency of the torsional vibrating element.

Another feature of my invention is the provision of means for causing the radial scanning device to scan an area of rectangular shape, or any other desired shape.

Another feature of my invention is the provision of a double radial scanning transmitter and double radial scanning receiver of television signals to produce a stereoscopic effect.

In the drawings,

Figure 1 is a side elevation of a radial scanner in accordance with the present invention;

Figure 2 is a front view of the device of Figure 1, looking from the right in that figure;

Figure 3 is a diagrammatic view of means for causing the rotating element of my radial scanner to produce an electric current of a frequency equal to the resonant frequency of the vibrating element and to supply this current to coils which excite the vibrating element;

Figure 4 is a diagrammatic View illustrating the manner in which my radial scanner will scan 5 an image;

Figure 5 is a diagrammatic view of means for causing my radial scanner to scan a rectangular area;

Figure 6 is a curve illustrating the envelope of 10 the grid potentials on the amplifier 5| in the system of Figure 5;

Figure 7 is a plan view of an alternative shape for my distorting condenser of Figure 5;

Figure 8 is a plan View of another alternative 15 shape for my distorting condenser of Figure 5;

Figure 9 is a schematic diagram of the transmitter of a radial scanning television system designed to produce stereoscopic images;

Figure 10 is a schematic diagram of a receiver 20 in my radial scanning television system for reproducing stereoscopic images;

Figure 11 is a diagrammatic View illustrating a viewing screen and the manner in which the images produced by the apparatus of Figure 10 25 are projected on such a screen; and

Figure 12 is a diagrammatic view of another manner of projecting images and using a double radial scanning system such as illustrated in Figures 9 and 10. 30

In Figures 1 and 2 I show a synchronous motor 21 which may be operated from a power network. Keyed to the shaft 22 of the motor is a disc 23 which may be of non-magnetic material. Carried on the disc 23 for rotation therewith is a 35 magnetic system consisting of a magnetic core 24 having four pole pieces 25, 26, 21 and 28 which are surrounded respectively by coils 29, 30, 3| and 32. Also mounted on the disc 23 are a pair of standards 33 and 34 on which is mounted 40 a torsional vibrating member 35 which may for example have a resonant frequency of vibration of five thousand cycles per second. Secured to the torsional member 35 is a crossbar 36 of magnetic material adapted to cooperate with the pole 5 pieces 26 and 28 to maintain the vibrating member in vibration. Attached to the crosspiece 36 is the mirror 31 which is the actual scanning element of my device.

The mirror 2| may be caused to rotate at any 5 desired frequency, say, for example, twenty-five revolutions per second. As it rotates it carries with it the disc 23 and the entire vibrating and magnetic system mounted on that disc, including all the elements numbered from 24 to 31, inclu- 55 sive. Slip rings (not shown) are provided in order to supply direct current to the coils 29 and 3!. Additional slip rings (also not shown) are provided in order to supply an alternating current to the coils 30 and 32 of a frequency equal to the resonant frequency of the torsional vibrating member 35. The apparatus of Figures 1 and 2 is to be used at both the transmitting and receiving ends of a television system and of course to cooperate with suitable light sources, optical systems, viewing screens, etc., such as are illustrated in connection with Figures 9 and 10. In one manner of using the apparatus of Figures 1 and 2 for transmitting, for example in the manner also shown in Figure 9, a source of light, optical system, photoelectric cell, amplifier, modulator, and wire or radio transmitting system would be used similar to the corresponding elements numbered and marked 68, 69, 13, Amp, Radio transmitter, 15, in Figure 9. In one manner of using the apparatus of Figures 1 and 2 in a receiver, for example as shown in Figure 10, there would be provided a radio receiver, amplifier and detector, source of light, optical system and viewing screen similar to corresponding elements numbered and marked 'l'i, Amp, Filter, 38, 82, 8E, '78, B8, in Figure 10.

Assume now that the motor 2% of Figures 1 and 2 is operating at twenty-five revolutions per second, that the torsional member 35 is vibrating at five thousand cycles per second, that the coils 25 and 21 are being supplied with direct current, and that the coils 26 and 28 are being supplied with alternating current of a frequency of dye thousand cycles per second, and that the apparatus is being used to reproduce an image which is represented by a spot of light modulated with signals corresponding to the image to be reproduced. The mirror 3'! will be vibrating and at the same time rotating about the axis of the shaft 22. At each half cycle of vibration it will scan a line illustrated by one of the diametric lines 38 of Figure l. One-half cycle later, that is of a second later, it will scan another line corresponding to the line 39 of Figure 4, etc., until in of a second the motor has completed a revolution and one frame of the image will be scanned. As will be seen, the image will appear to be circular and it may be viewed on a circular screen or it may be masked out by placing a black non-reflecting mask over the screen, such as illustrated by the cross-hatched area 20 of Figure 12. In using the device of Figures 1 and 2 for scanning an object .to be transmitted; the operation will, of course,

be substantially similar to, and well understood from, the foregoing description. In fact, as my system requires light-spot scanning at the transmitter the light spot will be caused to play over the object in radial lines just as the light beam used in reproduction plays over the screen in radial lines as described above in describing the use of the device for reception.

Of course, in describing my invention as using a particular frequency of rotation for the Of course, in describing my invention .as using a particular frequency of rotation for the motor 2! of twenty-five cycles and a particular frequency of vibration of the member 35 at five thousand cycles, I do not limit myself to any particular frequencies. However, in using these particular frequencies in reproducing an image on a screen two feet square the light spot would have to traverse approximately 34 inches on the .screen, or beyond the margins of the sides of the square. That is, in Figure 4, assuming that the sides of the square M are each 2 feet, when the light spot is scanning a line corresponding to a diagonal 42 of the square, the entire length of the line would be included within the viewed image, but when it is scanning a line corresponding to the line 43 perpendicular to two of the sides of the square, it would still be traversing this same distance of 34 inches but part of this distance would be outside of the area to be viewed. At the corners of the square, as along the line 42, successive radial excursions of the beam would be approximately 0.26 apart, while at the center of the square, that is along the line 43, successive radial excursions of the beam would be approximately 0.19" apart at the edge of the square viewing screen. If a vibrating frequency of 7500 cycles per second were used for the vibrating member 35 these distances would be reduced by one-third or to about 0.18" and 0.12" respectively.

Notwithstanding these relatively large spacings between the lines near the outer margins of the picture, there will be obtained compensating optical advantages due to the total absence of picture flicker and also a pleasing increase in illumination and definition near the central regions of the picture. The absence of picture flicker will be due to the fact that there is not in my system anything corresponding to a picture frequency. That is, there is no point at which the scanning of one frame begins or ends, nor an abrupt shift to a particular spot to start the scanning of the next frame. The scanning is continuous.

In Figure 3 I have illustrated one method of producing a current of a frequency corresponding to the resonant frequency of the vibrating system 35 without the use of slip rings, and in which the necessity for transmitting synchronizing impulses is eliminated provided the synchronous motors at the transmitting and receiving station are driven from the same power network. In this figure the disc 23, which in this case will be of magnetic material, has mounted on its periphery a plurality of poles 4% carrying coils 45. The disc, as before, has mounted on it the coils 3i? and 32 around the poles 26 and 28 to which the current of the resonant frequency of the vibrating system is to be supplied. In Figure 3 the disc 23 also has the torsional vibrating member 35 mounted thereon which again carries the crosspiece 36 and mirror 37. Around the rotating disc 23 is mounted a stator 45 on which are mounted a plurality of pole pieces 31 carrying stator coils 48 which are excited by a direct current. As the disc 23 revolves, a current of the resonant frequency of the vibrating member 35, or a sub-multiple thereof, is excited in the windings Q5 and is supplied direct to the windings 30 and 32. Of course the stator poles may be made of permanent magnets, avoiding the necessity of using windings or a source of direct current, and inasmuch as the mirror vibrating coils may be excited at a sub-multiple of the resonant frequency the stator poles may be few in number and therefore made relatively large.

I have illustrated in Figure 4 the circular nature of the image which will be produced in my system and in Figure 12 a non-reflecting mask which may be placed over the screen to cause only a rectangular portion thereof to be viewed.

In Figure 5 I illustrate apparatus for causing the radial scanner to scan an area of square shape. In this fiure I show again the disc 23,

torsional vibrating member 35, magnets and pole pieces 26, 30, 28, 32, crosspiece 36, mirror 31, pole pieces or teeth 44, stator 46, and poles and coils 41 and 48. The apparatus of Figure 5 so far named is similar to the apparatus of Figure 3 except that in Figure 5 there are no coils on the teeth 44. In this case the disc 23 would again be made of magnetic material. Another diiference between Figures 3 and 5 is that the alternating current of resonant frequency is, in the case of Figure 5, to be produced in the stator coils 48 instead of in the rotor coils 45 of Figure 3. This alternating current is brought out over the leads 49 and 58 and applied to the grid and filament respectively of an amplifying tube 5| which may be any conventional type of amplifier, for example a triode as shown.

Also keyed to the shaft 22 of the motor which drives the disc 23 is the armature 52 of a rotating condenser whose stator 53 of square shape is mounted so that the armature 52 rotates within the frame of the stator. This condenser 52, 53 has for convenience been shown separated from the motor 2| and disc 23 but as stated it will actually be mounted on the motor shaft. A brush 54 makes contact with the rotor of this condenser. The leads from the condenser 55 and 56 are connected to the grid-filament circuit of an oscillator 51 which may be of any conventional type, such as a triode as shown. The plate circuit of the oscillator is made oscillating by means of the variable condenser 58 connected across the lower portion of the coil 56. A resistance 68 shunted by a condenser 6| is connected in the plate circuit of the oscillator 51. By means of the rotating condenser 52, 53, a periodic change in the capacity of the oscillating grid circuit of the oscillator 51 occurs. This periodic change approximates in magnitude the geometric relationship between the square armature 53 and the motion of the rotating armature 52. This periodic change of capacity produces a corresponding change in the amplitude of the oscillations generated by the triode 51, which in turn is represented by a corresponding change in current in the plate circuit of this triode and consequently by a corresponding change in potential across the resistance 66. The resistance 66 is connected across the grid and filament of the amplifier 5! so that the grid of this amplifier is biased in proportion to the variations in potential across this resistance, and therefore in proportion to the capacity of the condenser 52, 53. A grid biasing battery 62 may be used to provide a desired initial bias of the amplifier 5|.

The current of the frequency of the vibrating member 35 supplied to the amplifier 5| is thus modulated in accordance with the shape and motion of the condenser 52, 53 and consequently in accordance with the shape of the image to be projected on the screen. The output of the amplifier 5| is supplied by means of a pair of brushes 63, 64 to the coils 30 and 32 through the slip rings 65 and 66. These brushes 63 and 64 are shown twice in this figure. At the right of the figure they are shown connected to the output circuit of the amplifier 5|, while at the left of the figure they are shown making contact with the slip rings 65 and 66. The current in the output of the amplifier 5| is supplied back tothe coils 30 and 32 by means of the brushes as shown at the left of the figure. The brushes 63, 64, slip rings 65, 66, coils 30, 32, crosspiece 36, and mirror 31 are shown at the right of the figure for convenience of illustration but actually there are only the single elements of these members as illustrated at the left of the figure where all of them, except, of course, the brushes, rotate with the disc 23. The beam of light is thereby caused to traverse a square area instead of a circular area. The useful illuminated area upon the viewing screen is thus economized and made more intense.

I have shown in Figure 5 a condenser having an armature 52 with a single arm, although I have also indicated in dotted lines the possibility of the use of an armature with four arms. Of course, any desired number may be used to get the desired modulating effect.

In Figure 6 I have indicated in graphical form the envelope of the potential on the grid of the amplifier 5| for the particular example chosen for explanation in connection with the showing of Figure 5. These potentials will vary in a form not sinusoidal but of the proper contour to produce the above described variation in the amplitude of the oscillating mirror 31 as it is spun around the axis of the synchronous motor.

In Figures '7 and 8 I have shown another method of varying the modulations to correspond with a desired viewing area in which I make the stator 53 of the condenser of various shapes to correspond with the shape of viewing area desired.

In Figure 9 I have illustrated my radialscanning television system in use as a transmitter 01 stereoscopic television images. In this figure I have shown two of my radial scanners consisting each of a motor 2|, disc 23, torsional vibrating member 35, mirror 31, and the other elements which cooperate with these as illustrated in Figure 1. The object to be scanned is illustrated at 61. I have a source of light 68 which is projected through a suitable optical system indicated at 69 upon the mirror 31 of the upper scanner and reflected in radial scanning lines upon the image 61 which is to be transmitted. I have a second source of light 10 projected by a suitable optical system indicated at 1| upon the lower mirror 31 of the other radial scanner. In order to shut out extraneous light I may provide a mask 12 with an opening just large enough to permit the two radial scanning cones of light to pass therethrough. The two radial scanners shown in this figure are turned at an angle pointing to the object 61 and separated laterally to permit the stereoscopic viewing of the object by the two vibrating mirrors 31. The light reflected from the light sources 68 and 10 is picked up respectively by two photoelectric cells 13 and 14 which are connected through suitable amplifiers and radio transmitters to the radiating antennas 15 and 16 respectively. It would, of course, be possible to use a single motor to operate the two radial scanners by suitable gearing and also to use a single radio transmitter and single antenna from which the two radio frequencies would both be radiated,

In Figure 10 I have illustrated a television receiver for my stereoscopic signals transmitted with the apparatus illustrated in Figure 9. In Figure 10 there is an antenna 11 in which the two frequencies transmitted from the apparatus of Figure 9 are received, a radio frequency amplifier, and two filter systems for separating the two frequencies, Each of these frequencies is supplied to an optical device, such, for example, as Kerr cells 18, 19. Light from suitable light sources 80 and 8| is projected by suitable optical systems such as lenses 82, 83 and Nicol prisms 84, 85

through the Kerr cells 1B, 19, onto two radial scanners similar to those illustrated in Figures 1 and 2, or Figure 3, which I have here indicated by the numbers 86, B1, and reflected from the mirrors of these radial scanners onto a viewing screen 88. The light reflected from the radial scanners of the transmitter of Figure 9 was caused to overlap and the cones of light from the radial scanners of Figure 10 are caused to overlap in the same manner as is illustrated in Figure 11. Here the overlap portion is indicated by the numeral 89. A mask may be provided to cause only a rectangular portion of the screen to appear in View, or a system such as that illustrated in Figure 5 may be used at both the transmitter and receiver to cause the radial scanners to scan areas of the desired shape.

It will be seen from Figure 11 that I thus obtain right and left images appropriately spaced on the viewing screen with a common overlap or region 89 illuminated by both pictures. In this manner I obtain a stereoscopic, quasi-stereoscopic, or depth effect, impossible where a single scanning system is employed. Of course, at the receiver I may also use a single motor and operate both scanners from it by suitable gearing, and this will still be possible even though I employ the system illustrated in Figure 5 for controlling the area of the projected image. I have indicated at 90 in Figure 11 a non-reflecting mask to restrict the viewing area,

I may also use my double radial scanning system, as illustrated in Figures 9 and 10, to increase the definition and light on a viewing screen by simply superimposing the images on one another, exhibiting them as a single square as illustrated in Figure 12. In this case I will place my transmitting scanners close together and cause them to scan the same area and also place my receiving scanners close together and cause them to scan the same area. I may cause the lines to be projected in any suitable angular relation to one another, as for example at right angles, so that the lines projected from different scanners will be projected along different lines of the screen at any instant. I may also cause the lines to interlace, thus getting twice the definition at the extremities of the image.

In place of the method above described for periodically varying the excursions of the mirror as it revolves, I may use the principle of beat frequencies, by employing two sources of high frequency current, both of which are impressed upon the coils of the vibrating magnet; one frequency may be 5000 cycles and the other 4900 cycles or one frequency may be 5050 and the other frequency 4950 cycles. The beat frequency between these two is cycles, which means that if the mirror is rotating at the rate of 25 revolutions per second, then 4 times for each revolution the mirror will be subject to a force of maximum amplitude, corresponding roughly to the corners of the square picture, and 4 times per revolution subject to a minimum impulse, corresponding to the 4 sides of the square of the picture frame. By this beat frequency principle the shape of the picture may be made to approximate a square.

I do not, of course, wish to limit myself to the precise details disclosed but only as indicated by the scope of the appended claims.

What is claimed is:

l. A radial scanner for a television system, comprising a rotating member, a pair of coils mounted on said member, a plurality of teeth mounted on the periphery of said member, a plurality of coils surrounding said teeth, means for exciting an alternating current in said coils surrounding said teeth, and means for supplying said current to said first mentioned coils.

2. A radial scanner for a television system comprising a rotating member, a vibrating member mounted on said rotating member, a pair of coils for exciting said vibrating member into vibration, means mounted on said rotating member for generating a current having a frequency equal to the resonant frequency of said vibrating member, and means for supplying said current to said coils.

3. A television system comprising a rotating member, a vibrating member mounted on said rotating member, means mounted on said rotating member for exciting said vibrating member, means mounted on said rotating member whereby it acts as the rotor of an alternator, a stator for said alternator, and means for supplying the currents produced by said alternator to said exciting means.

4. A radial scanner for a television system com;

prising a rotating member, a vibrating member mounted on said rotating member, means for causing said vibrating member to vibrate, a condenser rotor mounted on said rotating member, a condenser stator mounted adjacent to said condenser rotor, and means responsive to variations in capacity of said condenser to modulate the amplitude of vibration of said vibrating member.

5. A radial scanner for a television system comprising a rotating member, a vibrating member mounted on said rotating member, a condenser having a rotor mounted on said rotating member, an oscillator, means for causing said condenser to vary the amplitude of oscillations of said oscillator, a resistance connected in the circuit of said oscillator, means cooperating with said rotating member to generate a current having a frequency equal to the resonant frequency of said vibrating member, an amplifier supplied with said current, electrical connections between said amplifier and the resistance in the circuit of said oscillator whereby said current is modulated in proportion to the variation in potential across said resistance, and means for supplying said modulated current to the means which causes said vibrating member to vibrate.

6. A television system comprising a rotating member, a vibrating member mounted on said rotating member, means for exciting said vibrating member, means mounted on said rotating member whereby said rotating member acts as the rotor of an alternator, a stator for said alternator, means for distorting the electrical currents produced in said alternator, and means for supplying said distorted currents to said exciting means.

7. A television system comprising a rotating member, a vibrating member mounted on said rotating member, means for exciting said vibrating member, a stator, means whereby said rotating member causes electrical currents to be generated in said stator, means for distorting said currents, and means for supplying said distorting currents to said exciting means.

8. A television system comprising a rotating member, a vibrating member mounted on said rotating member, means mounted on said rotating member for exciting the said vibrating member, means for generating electrical current of a frequency equal to the resonant frequency of said Vibrating member, means for amplifying said current, means mounted on said rotating member for modulating the current in said amplifier, and means for supplying said modulated current to said exciting means.

9. In a television system an oscillating mirror, and means for moving the aids 'of oscillation continuously in one direction in a single inane.

10. In a television scanning system, a tortional member which moves in one plane, a mirror mounted on said member, and means for moving said tortional member continuously in one direction.

11. In a television scanning system, a tortional member the axis of which is designed to 5 move in one plane only, a mirror mounted on said member, and means for moving the torti'onal member continuously in one direction.

LEE DE FOREST. 

